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I have a thread which has an incoming job queue (a LinkedList containing job descriptions). The thread blocks with wait() on the queue when there's no job to work on. An external job dispatcher object awakes it with notify() when it places new jobs on the queue.
At shutdown of my program i call interrupt() on the Thread. This raises InterruptedException when the Thread awaits for jobs in wait(). My question is: what will happen if i interrupt the Thread while it's not blocking but doing some kind of work, the processed item was the last in the queue (so queue is now empty) and execution pasts the isInterrupted() check before the interrupted flag is set so it calls wait() again? Will it throw an InterruptedException because the interrupted flag has already been set or the thread waits forever because new jobs will never arrive to the queue and there's no one to interrupt the wait?
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Interrupting a thread is a state-safe way to cancel it, but the thread itself has to be coded to pay attention to interrupts. Long, blocking Java operations that throw InterruptedException will throw that exception if an . interrupt() occurs while that thread is executing.
A thread that is in the sleeping or waiting state can be interrupted with the help of the interrupt() method of Thread class.
Calling Thread. interrupt() is a way to tell the thread to stop what it is doing. If the thread is in a blocking call, the blocking call will throw an InterruptedException, otherwise the interrupted flag of the thread will be set. A Thread or a Runnable that is interruptible should check from time to time Thread.
3. What Is an InterruptedException? An InterruptedException is thrown when a thread is interrupted while it's waiting, sleeping, or otherwise occupied. In other words, some code has called the interrupt() method on our thread.
Though this is quite an old question, but I would want to add that if you call Thread.currentThread().interrupt() method during lock.wait() (while thread is in WAITING state), it doesn't mean that thread will internally have InterruptedException thrown immediately, first thread will get in BLOCKED state (it becomes awakened as with lock.notify()/notifyAll() call from another thread, that allows it to compete for a shared lock) with interruption flag set to true, maybe after some period of time only after acquiring lock again (sometimes quite considerable amount of time) it can throw an InterruptedException (without lock it cannot proceed, even handling an exception).
package com.company;
public class Main {
public static void main(String[] args) {
final Object lock = Main.class;
// three simple threads
Thread th1 = new Thread(() -> {
synchronized (lock) {
for (int i = 0; i < 15; i++) {
sleepWithoutException(100);
System.out.println("th1 is doing some job!");
}
}
});
Thread th2 = new Thread(() -> {
synchronized (lock) {
for (int i = 0; i < 15; i++) {
sleepWithoutException(100);
System.out.println("th2 is doing some job!");
}
}
});
Thread th3 = new Thread(() -> {
synchronized (lock) {
for (int i = 0; i < 15; i++) {
sleepWithoutException(100);
System.out.println("th3 is doing some job!");
}
}
});
// thread which will be in WAITING state after 1 second
Thread th4 = new Thread(() -> {
synchronized (lock) {
try {
sleepWithoutException(500);
lock.wait();
System.out.println("Continued");
} catch (InterruptedException e) {
System.out.println("interrupted! " + e);
System.exit(1);
}
}
});
// execution
th4.start();
sleepWithoutException(100);
th1.start();
th2.start();
th3.start();
// thread which will monitor states of other threads
new Thread(() -> {
long start = System.currentTimeMillis();
for (int i = 0; i < 1000_000; i++) {
sleepWithoutException(100);
System.out.println("-------------------------------------------------");
System.out.println("step: " + i + " , timeElapsed: " + (System.currentTimeMillis() - start));
if (i == 10) {
th4.interrupt();
}
System.out.println(
th1.getState() + " " + th1.isInterrupted() + "\n" +
th2.getState() + " " + th2.isInterrupted() + "\n" +
th3.getState() + " " + th3.isInterrupted() + "\n" +
th4.getState() + " " + th4.isInterrupted()
);
}
}).start();
}
public static void sleepWithoutException(long time) {
try {
Thread.sleep(time);
} catch (InterruptedException e) {
System.out.println("fallen in sleep" + e);
}
}
}
see log below, as you can see other threads continue to work while th4 in BLOCKING state with flag isInterrupted is set to true (after a call of Thread.currentThread().interrupt() method)
-------------------------------------------------
step: 0 , timeElapsed: 101
BLOCKED false
BLOCKED false
BLOCKED false
TIMED_WAITING false
-------------------------------------------------
step: 1 , timeElapsed: 201
BLOCKED false
BLOCKED false
BLOCKED false
TIMED_WAITING false
-------------------------------------------------
step: 2 , timeElapsed: 301
BLOCKED false
BLOCKED false
BLOCKED false
TIMED_WAITING false
-------------------------------------------------
step: 3 , timeElapsed: 401
BLOCKED false
BLOCKED false
TIMED_WAITING false
WAITING false
th3 is doing some job!
-------------------------------------------------
step: 4 , timeElapsed: 502
BLOCKED false
BLOCKED false
TIMED_WAITING false
WAITING false
th3 is doing some job!
-------------------------------------------------
step: 5 , timeElapsed: 602
BLOCKED false
BLOCKED false
TIMED_WAITING false
WAITING false
th3 is doing some job!
-------------------------------------------------
step: 6 , timeElapsed: 703
BLOCKED false
BLOCKED false
TIMED_WAITING false
WAITING false
th3 is doing some job!
-------------------------------------------------
step: 7 , timeElapsed: 803
BLOCKED false
BLOCKED false
TIMED_WAITING false
WAITING false
th3 is doing some job!
-------------------------------------------------
step: 8 , timeElapsed: 904
BLOCKED false
BLOCKED false
TIMED_WAITING false
WAITING false
th3 is doing some job!
-------------------------------------------------
step: 9 , timeElapsed: 1004
BLOCKED false
BLOCKED false
TIMED_WAITING false
WAITING false
th3 is doing some job!
-------------------------------------------------
step: 10 , timeElapsed: 1105
BLOCKED false
BLOCKED false
TIMED_WAITING false
WAITING true
th3 is doing some job!
-------------------------------------------------
step: 11 , timeElapsed: 1205
BLOCKED false
BLOCKED false
TIMED_WAITING false
BLOCKED true
th3 is doing some job!
-------------------------------------------------
step: 12 , timeElapsed: 1306
BLOCKED false
BLOCKED false
TIMED_WAITING false
BLOCKED true
th3 is doing some job!
-------------------------------------------------
step: 13 , timeElapsed: 1406
BLOCKED false
BLOCKED false
TIMED_WAITING false
BLOCKED true
th3 is doing some job!
-------------------------------------------------
step: 14 , timeElapsed: 1507
BLOCKED false
BLOCKED false
TIMED_WAITING false
BLOCKED true
th3 is doing some job!
-------------------------------------------------
step: 15 , timeElapsed: 1607
BLOCKED false
BLOCKED false
TIMED_WAITING false
BLOCKED true
th3 is doing some job!
-------------------------------------------------
step: 16 , timeElapsed: 1708
BLOCKED false
BLOCKED false
TIMED_WAITING false
BLOCKED true
th3 is doing some job!
-------------------------------------------------
step: 17 , timeElapsed: 1808
BLOCKED false
BLOCKED false
TIMED_WAITING false
BLOCKED true
th3 is doing some job!
-------------------------------------------------
step: 18 , timeElapsed: 1909
BLOCKED false
TIMED_WAITING false
TERMINATED false
BLOCKED true
th2 is doing some job!
-------------------------------------------------
step: 19 , timeElapsed: 2009
BLOCKED false
TIMED_WAITING false
TERMINATED false
BLOCKED true
th2 is doing some job!
-------------------------------------------------
step: 20 , timeElapsed: 2110
BLOCKED false
TIMED_WAITING false
TERMINATED false
BLOCKED true
th2 is doing some job!
-------------------------------------------------
step: 21 , timeElapsed: 2211
BLOCKED false
TIMED_WAITING false
TERMINATED false
BLOCKED true
th2 is doing some job!
-------------------------------------------------
step: 22 , timeElapsed: 2311
BLOCKED false
TIMED_WAITING false
TERMINATED false
BLOCKED true
th2 is doing some job!
-------------------------------------------------
step: 23 , timeElapsed: 2412
BLOCKED false
TIMED_WAITING false
TERMINATED false
BLOCKED true
th2 is doing some job!
-------------------------------------------------
step: 24 , timeElapsed: 2512
BLOCKED false
TIMED_WAITING false
TERMINATED false
BLOCKED true
th2 is doing some job!
-------------------------------------------------
step: 25 , timeElapsed: 2613
BLOCKED false
TIMED_WAITING false
TERMINATED false
BLOCKED true
th2 is doing some job!
-------------------------------------------------
step: 26 , timeElapsed: 2713
BLOCKED false
TIMED_WAITING false
TERMINATED false
BLOCKED true
th2 is doing some job!
-------------------------------------------------
step: 27 , timeElapsed: 2814
BLOCKED false
TIMED_WAITING false
TERMINATED false
BLOCKED true
th2 is doing some job!
-------------------------------------------------
step: 28 , timeElapsed: 2914
BLOCKED false
TIMED_WAITING false
TERMINATED false
BLOCKED true
th2 is doing some job!
-------------------------------------------------
step: 29 , timeElapsed: 3015
BLOCKED false
TIMED_WAITING false
TERMINATED false
BLOCKED true
th2 is doing some job!
-------------------------------------------------
step: 30 , timeElapsed: 3115
BLOCKED false
TIMED_WAITING false
TERMINATED false
BLOCKED true
th2 is doing some job!
-------------------------------------------------
step: 31 , timeElapsed: 3216
BLOCKED false
TIMED_WAITING false
TERMINATED false
BLOCKED true
th2 is doing some job!
-------------------------------------------------
step: 32 , timeElapsed: 3316
BLOCKED false
TIMED_WAITING false
TERMINATED false
BLOCKED true
th2 is doing some job!
-------------------------------------------------
step: 33 , timeElapsed: 3417
TIMED_WAITING false
TERMINATED false
TERMINATED false
BLOCKED true
th1 is doing some job!
-------------------------------------------------
step: 34 , timeElapsed: 3517
TIMED_WAITING false
TERMINATED false
TERMINATED false
BLOCKED true
th1 is doing some job!
-------------------------------------------------
step: 35 , timeElapsed: 3618
TIMED_WAITING false
TERMINATED false
TERMINATED false
BLOCKED true
th1 is doing some job!
-------------------------------------------------
step: 36 , timeElapsed: 3718
TIMED_WAITING false
TERMINATED false
TERMINATED false
BLOCKED true
th1 is doing some job!
-------------------------------------------------
step: 37 , timeElapsed: 3819
TIMED_WAITING false
TERMINATED false
TERMINATED false
BLOCKED true
th1 is doing some job!
-------------------------------------------------
step: 38 , timeElapsed: 3919
TIMED_WAITING false
TERMINATED false
TERMINATED false
BLOCKED true
th1 is doing some job!
-------------------------------------------------
step: 39 , timeElapsed: 4019
TIMED_WAITING false
TERMINATED false
TERMINATED false
BLOCKED true
th1 is doing some job!
-------------------------------------------------
step: 40 , timeElapsed: 4120
TIMED_WAITING false
TERMINATED false
TERMINATED false
BLOCKED true
th1 is doing some job!
-------------------------------------------------
step: 41 , timeElapsed: 4220
TIMED_WAITING false
TERMINATED false
TERMINATED false
BLOCKED true
th1 is doing some job!
-------------------------------------------------
step: 42 , timeElapsed: 4321
TIMED_WAITING false
TERMINATED false
TERMINATED false
BLOCKED true
th1 is doing some job!
-------------------------------------------------
step: 43 , timeElapsed: 4421
TIMED_WAITING false
TERMINATED false
TERMINATED false
BLOCKED true
th1 is doing some job!
-------------------------------------------------
step: 44 , timeElapsed: 4522
TIMED_WAITING false
TERMINATED false
TERMINATED false
BLOCKED true
th1 is doing some job!
-------------------------------------------------
step: 45 , timeElapsed: 4622
TIMED_WAITING false
TERMINATED false
TERMINATED false
BLOCKED true
th1 is doing some job!
-------------------------------------------------
step: 46 , timeElapsed: 4723
TIMED_WAITING false
TERMINATED false
TERMINATED false
BLOCKED true
th1 is doing some job!
-------------------------------------------------
step: 47 , timeElapsed: 4823
TIMED_WAITING false
TERMINATED false
TERMINATED false
BLOCKED true
th1 is doing some job!
interrupted! java.lang.InterruptedException
Process finished with exit code 1
yes, your interrupted thread will throw an InterruptedException upon calling wait(). this is pretty simple to test for yourself.
public class TestInt {
public static void main(String[] args) throws Exception
{
Thread.currentThread().interrupt();
synchronized(TestInt.class) {
TestInt.class.wait();
}
}
}
also, note the javaodc for Object.wait():
InterruptedException - if any thread interrupted the current thread before or while the current thread was waiting for a notification. The interrupted status of the current thread is cleared when this exception is thrown.
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